CEPHALOPODA. 417 



Class V. CEPHALOPODA.* 



With well-marked head, a circle of processes bearing suckers or 

 tentacles round the mouth, and a funnel composed of two separate 

 or fused halves. The genital coelom is continuous ivitfcjhe peri- 

 cardial. Dioecious. 



The Cephalopoda are symmetrical animals with a much-shortened 

 antero-posterior axis, and with a strongly -developed visceral sac, 

 which has undergone neither torsion nor asymmetrical development, 

 and which is, except in Nautilus, unprotected by an external shell. 

 The mantle-fold is circular and the mantle -cavity is especially 

 developed on the posterior side of the visceral sac; in it are placed 

 the ctenidia, either two (Dibranchiata) or four (Tetrabranchiata), 

 and into it open the median anus, the ink-sac, the paired kidneys, 

 and the genital duct. There are always processes round the 

 mouth, which are either lobe-like and carry tentacles as in the 

 Tetrabranchiates, or are arm -like and carry suckers as in the 

 Dibranchiates. They are active, voracious animals, with a complex 

 organization, highly developed sense-organs, and often possessed of 

 considerable intelligence. The Cephalopods are marine animals, 

 some frequenting the coast, others the high seas, and some the 

 floor of the ocean to a depth of nearly 2000 fathoms. About 400 

 species are known. They feed on the flesh of animals, especially 

 Crustacea, and some of them attain a great size.f The flesh is 

 eaten, and the colouring matter of the ink-sac (sepia) and the dorsal 

 shell (os sepiae or cuttle-bone) are used by man. The remains of 

 Cephalopods occur in all formations from the Cambrian, and con- 

 stitute important characteristic fossils (Belemnites, Ammonites). 



* Ferussac et d'Orbigny, " Histoire naturelle generate et particuliere des 

 Cephalopodes acttabuliferes vivants et fossiles," Paris, 1835-45. J. B. Verany, 

 " Mollusques mediterranes observes, etc., d'apres le vivant," l e Partie, Genes, 

 1847-51. H. Milller, " Ueber das Mannchen von Argonauta argo u. die Hec- 

 tocotylen," Z. f. w. Z., 1855. Jap. Steenstrup, " Hectocotylus dannelsen hos 

 Octopodsl., etc.," K. Danks. Vidensk. Selskabs Skrifter, 1856; translated in 

 Archiv. f. Naturgesch., 1856. C. Grobben, " Morphologische Studien lib. den 

 Harn-u. Geschlechtsapparat, etc., der Cephalopoden," Arb. a. d. Zool. Inst. 

 Wien, 5, 1884. W. E. Hoyle, "Report on the Cephalopoda," Challenger 

 Reports, vol. 16, 1886. J. Brock, "Zur Anat. n. Syst. d. Cephalopoden," 

 Z. f. w. Z., 36, 1882. P. Pelseneer, " Sur la value morphologique des bras et la 

 composition du syst. nerv. cent. d. Cephalopodes," Arch. Biol. 8, 1888. 

 Milne-Edwards et Valenciennes, " Obs. sur la circulation chez les Mollusques," 

 Mem. Acad. Sci. Paris, 20, 1840. Vigelius, " Ueb. d. excretionssystem der 

 Cephalopoden," Niederl. Arch. f. Zool., 5, 1880. Milne -Ed wards, "Sur les 

 spermatophores des Cephalopodes," Ann. Sci. Nat. Zool. (2), 18, 1842. 



f Specimens of Architeuthis have been taken measuring from apex of visceral 

 sac to end of extended arms more than 50 feet, and with eyes 15 inches 

 across. 



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